1. Field of the Invention
The present invention relates generally to organic electroluminescent displays, and more particularly to a structure of a cathode rampart of an organic electroluminescent display.
2. Description of the Related Art
With the advent of the information technology age, there is an increasing demand for high-quality electro-optical displays, in which liquid crystal displays (LCD) are the most popular. A LCD backlight module comprising a light guide and a reflective plate is utilized for introducing the light beams, emitted from the cold cathode fluorescent lamp, vertically to the liquid crystal display panel, in which the liquid crystal contained therein controls the illuminance of the LCD. Conventional LCD has a limited view angle and requires very complicated manufacturing processes, which result in high manufacturing costs and relatively low yields. However, organic electroluminescent displays (OELD) have larger view angle and can be produced through less complex manufacturing process. These advantages are based on the self-luminance of the organic elements in the organic electroluminescent displays, which results in the unrestricted visual angles, more natural colors displayed, increased operational temperature range and shorter response time.
Organic electroluminescent displays generally include cathodes, organic electroluminescent materials and anodes, which are stacked in sequence on a substrate of glass. The cathodes and the anodes are respectively composed of a plurality of electrodes disposed in a parallel stripes formation, and the cathodes and anodes are configured perpendicular to each other. Organic electroluminescent materials are disposed at the intersections of the cathodes and the anodes, and are separated by insulating materials. Accordingly, the cathodes, the organic electroluminescent materials and the anodes form a three-layer structure disposed on the substrate. When a voltage difference between the cathodes and the anodes is present, the organic electroluminescent material emits light beams.
The metal electrodes of the cathodes are coated through evaporation on the organic electroluminescent material after the organic electroluminescent material and the insulating materials are formed. However, the cathodes composed of metal electrodes are easily diffused along the gaps between the organic electroluminescent material and the insulating materials during the formation step. Once the cathodes contact the anodes, it will short circuit and the organic electroluminescent materials between the cathodes and the anodes can not emit light.
If foreign particles fall aside the insulating materials as defects before the electrodes of the cathode are formed by coating through evaporation, metal materials will be formed around the foreign particles during the formation step and a short circuit is likely between neighboring metal electrodes.
Furthermore, during the manufacturing process of full-color organic electroluminescent displays (FOELD), it is necessary to utilize shadow masks for partially masking the organic electroluminescent material. After the organic electroluminescent material layer for emitting light beams of one color is coated on the anodes, the shadow masks are moved so as to form another organic electroluminescent material layer for emitting light beams of another color. In this case, the shadow masks will contact the insulating materials directly during the formation of the second organic electroluminescent material layer. This will cause the insulating materials to be peeled off and deteriorate the organic electroluminescent material.
In the prior art, forming a plurality of cathode ramparts in the direction perpendicular to anode electrodes to separate cathode electrodes arranged in parallel from each other is disclosed. With the exposure at the side of the cathode ramparts, since the exposure is focused mostly at the upper portion of the cathode ramparts, the portion of the cathode ramparts adjacent to the anode electrodes is not of sufficiently cross-linking and consequently the mechanical performance thereof is not significantly high. This results in the cathode ramparts being easily peeled off while contacting the shadow masks due to the deterioration of the adhesion between the ramparts and the substrate.
If the adhesion between cathode ramparts and substrate is strengthened by revising the parameters in photolithography process, the geometry of the cathode ramparts can not be effectively used as a mask during the coating of the cathode electrodes through evaporation.